There has hitherto been disclosed a PWM inverter device including first means for generating a three-phase modulation switching signal to perform a switching operation for each of phases of a PWM inverter and second means for generating a two-phase modulation switching signal that eliminates need of the switching operation for one of the phases. The PWM inverter device switches between the two means based on an amplitude value of inverter output voltages (see, for example, Patent Literature 1).
Further, there has been disclosed a power converter, which reduces noise and vibration by using lower solid two-phase modulation or upper solid two-phase modulation when a modulation factor being an amplitude of a duty command signal to a power-supply voltage is larger than a first predetermined value and by controlling a neutral voltage so that the neutral voltage becomes approximately half of a capacitor voltage when the modulation factor is equal to or smaller than the first predetermined value (see, for example, Patent Literature 2).